The subject of the invention is a device for controlling the stopping of a shrouding product driven by an asynchronous motor having a phase-shifting capacitor (1) stopping the motor when the shrouding product encounters an abutment or an obstacle and utilizing for this purpose at least one operating parameter of the motor so as to detect the appearance of a resisting overtorque.
Such a device is used in particular to control the stopping of the motor of a roller blind or shutter winding tube when the roller blind or shutter reaches an abutment in the fully wound up position. It may also serve to stop the descent of a roller blind or the closure of a door when this shrouding product encounters an obstacle in its closure motion or control the stopping of the motor when such a shrouding product reaches an abutment in the completely closed position.
Several devices functioning according to this principle are known. These devices are differentiated by the parameter measured and the manner in which it is measured and utilized. In the device according to patent DE 42 11 495, the content of which is incorporated by reference, the voltage across the terminals of the windings of the motor is measured. In patent GB 2 168 497, the content of which is incorporated by reference, the parameters measured are the principal current and the principal voltage. Patents FR 2 749 714, 2 649 260 and 2 685 289, the contents of which are incorporated by reference, disclose devices measuring the voltage across the terminals of the phase-shifting capacitor. The device described in patent EP 0 716 214, the content of which is incorporated by reference, uses the current in the principal winding and the current in the auxiliary winding of the motor as parameters. Finally, from patent DE 43 12 987, the content of which is incorporated by reference, it is known practice to measure the voltage across the terminals of the auxiliary winding of the motor.
All these devices show evidence of creativity and ingenuity as regards the means of detection, the accuracy of detection and compensation for the influence of the temperature of the motor, but they all have a major drawback in the case where detection must be both sensitive and reliable, especially in the case of doors or other compensated-weight shrouding products where the motor provides little torque, since this detection is perturbed and falsified by the voltage drops in the local network, these voltage drops modifying the value of the parameters measured. This perturbation results in unexpected stoppages, disturbances and learning errors due to confusing a drop in the measured parameter (due to the appearance of a resisting overtorque) and a drop in the value of the measured parameter (due to a drop in the voltage of the local network) due, for example, to a brief network overload (due, for example, to the starting up of a large electrical consumption device or to a natural phenomenon such as a thunderstorm). Such confusion may have disastrous consequences on a canvas. For example, if a strong wind blows up while a canvas is unfurled, an automatic controller for protecting against the wind detects and instructs the motorization to wind the canvas up fully. If this strong wind is accompanied by a thunderstorm and if the lightning should strike a distribution line, then there will inevitably be variations in the local network supply which might perturb the motor. If the detection device is sensitive, a quality which is required so as not to harm the shrouding product in the end-of-winding position, then there will very probably be an erroneous detection of end of winding and a stoppage of the motor while the canvas is still partially unfurled, which may have disastrous consequences.
In the case of a shutter or roller blind, the stopping of which in the fully unwound position is controlled by counting pulses starting from the wound-up position, a drop in the voltage in the local network may also have serious consequences when the point of stoppage in the fully wound up position is confused with a stoppage in an intermediate position due to this drop in the voltage of the supply. This is because the counting will take place starting from the position of intermediate stoppage as if it were the fully wound up position, so that the device for controlling the stoppage of the motor will want to continue the unwinding beyond the fully unwound position, and this could cause damage to the apparatus.
The purpose of the invention is to obviate these drawbacks.